Mediterranean/Atlantic
Climate: Many British divers still head for Mediterranean waters despite the lure of more exotic seascapes. It offers warmwater diving with summerea temperatures up to a balmy 25-26°C in places. Winter temperatures drop a little, but still make for comfortable diving in a wetsuit. The climate is equable, with hot summers, pleasant springs and autumns and cool winters.
Winds: Spring and summer can bring the hot, dusty sirocco wind from the Sahara to Malta, Italy and Greece, while France sometimes gets the strong mistral, and the ghibli blows across from north-west Africa towards Spain.
The Atlantic coasts of southern Spain and Portugal have Mediterranean climates, but the water is a little cooler, at an average 16-18°C in summer. The Canaries and Madeira also have Mediterranean-style climates with warmer winters than the mainland but much colder water thanks to the cool Atlantic currents.
Health: Malaria precautions are needed only if travelling east of Antalya in Turkey. Hepatitis is a risk in Turkey and Tunisia, where typhoid immunisation is also recommended.
Middle East
The Red Sea offers great diving all year round. The region has hot, dry summers and mild, dry winters with cold nights. The hot, dusty Khamsin wind blows from the Sahara in April. Winds are generally at least Force 4 and can reach Force 8 or 9 in late spring and early summer, caused by the extremes of day and night temperatures of the surrounding desert.
Temperatures: Eilat and Sharm el Sheikh have similar climates, with average daytime temperatures of 21°C in winter and up to 40° or more in summer. Hurghada is generally a little cooler in summer. Water temperature also varies by season and between the northern and southern Red Sea, averaging 21°C in January and 26°C in August, but as high as 28-34°C in places. Humidity is higher in the southern Red Sea, particularly between December and May. Oman is very hot in June and July, with temperatures up to 39°C and the sea at its warmest and clearest.
Summer is a good time to go to the region, if you can stand the heat, for a rare chance to dive with a whale shark. They venture up as far as Eilat and are often seen off the Straits of Tiran. But their presence can mean that visibility is affected, because of the plankton that attracts them.
Health: Malaria is a risk in the southern Red Sea and in Yemen and Oman. Precautions should be taken against cholera, hepatitis, typhoid and polio throughout the region.
Indian Ocean
The Maldives stretch 600 miles to the Equator and have a hot tropical climate with daytime temperatures above 30*C year-round and night temperatures rarely below 25*C. There are two rainy seasons - the SW monsoon from May to October (which can bring heavy rain and strong winds, particularly in June and July), and the NW monsoon from November to April, the best time to visit. Plankton blooms from December to May can cut visibility, but increase the chance of seeing manta rays and whale sharks, especially in the east. Water temperatures in the Maldives and also the Seychelles can reach 30*C.
The Seychelles offer year-round diving, as they lie outside the cyclone belt. However they do get monsoon rains from November to February, with NE trade winds, which can bring rough seas. June to August are the driest and coolest months, although the temperature rarely falls below 24*C. March to May and September to November are best for diving, with calmer seas and clearer visibility.
Mauritius has a cyclone season from December to March, when rainfall and temperatures are highest. Temperatures reach 30*C in January, falling to 24*C in July and August. Sea breezes can blow all year, particularly on the east coast.
The Comores has a similar cyclone season to Mauritius, with a hotter and wetter climate. Best diving is from April to September.
Kenya's tropical climate is tempered by monsoon winds. Wettest and hottest times are March to June and October to December. Currents outside the barrier reef and through the Pemba Channel can be very strong. Whale sharks can be seen at any time but especially from November to January.
South Africa's Atlantic Ocean sites around Cape Town, where humpback whales can be seen from August to December, are best dived during the southern summer months between November and April. Its Indian Ocean dive sites include Aliwal Shoal, with ragged-tooth sharks from mid-July to early November.
Health: Malaria and yellow fever are prevalent in some areas and precautions are advised against cholera, typhoid, polio and hepatitis in most countries.
Caribbean/Atlantic
Climate: Diving in the Caribbean is excellent throughout the year, but ignore the hurricane season (June to November) at your peril. A friend had his diving operation in Dominica reduced to rubble in one hurricane in the late '70s. The region offers warmwater diving, with sites on protected Caribbean coasts marginally warmer than those facing the Atlantic rollers.
Temperatures: Water temperatures vary little throughout the Caribbean, ranging from around 24°C in winter to 30*C in summer, while air temperatures range from 21°C to 32°C. The Bahamas and Florida Keys have similar water temperatures thanks to the Gulf Stream, which sweeps up past the east coast of North America to Bermuda and on across the Atlantic to warm our shores. It is the errant Gulf Stream that results in near-Caribbean water temperatures of as much as 30°C for Bermuda in summer and as low as 13°C in winter when it veers away. Needless to say, the Bermuda diving season runs only from March to November.
Rainfall: Expect plenty of rain in the tropical Caribbean and Florida summer months, but it will often fall in heavy, squally afternoon showers which last only an hour or so. Mountainous islands and those affected by river run-offs, such as Tobago with the Orinoco River, will inevitably suffer reduced visibility in the rainy summer season.
Migrations: Different times of the year offer different viewing possibilities for dolphins and whales. In the Grenadines pilot and humpback whales can be seen from April to November, while up to 100 humpbacks spend the winter just north of Tortola in the British Virgin Islands and sperm whales live off Dominica, Martinique and Guadaloupe.
Health: Typhoid and polio precautions are recommended for travel anywhere in the Caribbean, while malaria is found in parts of Haiti and the Dominican Republic as well on fringing mainland coasts.
Central/N America
Central America: The Caribbean coasts of Mexico (Cancun and Cozumel), Belize and Honduras are sub-tropical, with hot and dry weather from January to April and monsoon-like summers, with water temperatures similar to those of the Caribbean islands. The Pacific coasts of Mexico and Costa Rica also have wet summers, with relatively constant air temperatures. The waters of Costa Rica and Cocos Island drop to 20*C in winter but rise to 24-28*C from April to January.
USA: From Baja California up the US West Coast the climate is mild and arid, other than in winter. The water is much colder off Monterey, dipping to a chilly 10*C in winter because of currents that well up from the oceans. This is why the sea-life is so prolific. Visibility is best in autumn.
Canada: Further north still, British Columbia's seas barely reach 10*C. And if you want to get the best visibility you have to brave the snow showers and squalls of winter. But the chance of an encounter with a giant octopus, wolf eel or killer whale should warm any diver's heart.
Health: Typhoid, polio, hepatitis, yellow fever and malaria precautions are recommended for Central America.
Far East
Climate: Thailand, Malaysia and Indonesia have similar climates, with temperatures year-round between 30 and 32°C and water in the 26-30°C range. The SW monsoons in the Andaman Sea can bring heavy rain and rough seas from May to October. To the east of the region, NW monsoon rains occur from November to February.
Indonesia: The best time to dive Sipadan, off the coast of the Malaysian Borneo state Sabah, is from mid-February to mid-December, when visibility can reach 60m. August and September are when green sea turtles lay their eggs. The SE monsoon from June to September brings the driest and calmest weather to Indonesia's diving areas, while the NW monsoon brings the main rains and rough seas between December and March, although rainstorms can occur all year.
The Philippines has water temperatures ranging from 24*C in winter up to 31*C in summer. A tropical climate with sea breezes, September to April are the best months to visit the five main dive regions after the June-September rainy season, when typhoons sometimes occur and strong winds cut visibility.
Health: Malaria, cholera, typhoid and polio are all endemic in the region.
Australia/Pacific
Micronesia, including Truk and Palau, has consistent air and water temperatures averaging 28°C. August to November is the rainy season, while May and June can suffer plankton blooms that dent the normally tremendous visibility.
Papua New Guinea has a tropical equatorial climate, with the north getting torrential rains during the NW monsoon from November to March. The southern swamplands have the lowest rainfall but are humid and oppressive all year. The waters are always warm, particularly in the more sheltered Bismarck Sea.
Australia: Most diving is off the tropical Queensland coast, where the rainiest months are January to April. Off Western Australia the Ningaloo Reef offers the chance between March and June to dive with whale sharks attracted by spawning coral. Other migrations include humpback whales from August to the end of November and manta rays in July and August, while summer also brings loggerhead, green and hawksbill turtles to lay their eggs. Diving is year-round, with warm waters and air temperatures from 26°C in winter to 35°C in summer.
Fiji's soft coral gardens are best seen between April and January, avoiding the plankton blooms of February and March. Air and water temperatures range from 24°C in the winter months (May to October) and 27°C in summer, when Fiji gets most of its rain.
New Zealand's North Island enjoys a subtropical climate with warm, humid summers, especially in the far north, called Northland. The South Island has a maritime climate and snow can fall at ground level in Fjordland in winter. The warmwater South Equatorial Current, which sweeps down Australia's east coast then across the Tasman Sea, helps to raise temperatures by a few degrees in Fjordland, leading to a mixture of coldwater and and warmwater species. The northern part also bathes the Poor Knights islands off North Island's east coast, but not the coast itself, making for much warmer diving and a sub-tropical flavour to the fauna. But during the southern hemisphere spring and summer it can also lead to the 30-60m visibility being badly affected by plankton blooms. The best time to visit is late summer to early winter.
Hawaii is a tropical year-round Pacific destination with warm seas and little difference between the summer and winter climate, although it has some rain from December to February. Maui and the neighbouring islands plus the Big Island have the best water conditions. Summer and autumn offer the best visibility, at up to 60m.
The Galapagos: Ecuador's islands have some of the world's most unusual sea life, thanks to the cool waters that attract both tropical and coldwater species. Diving, from liveaboards, is year-round off these strange, sub-tropical islands where January to April are the hottest months.
Health: Malaria precautions are recommended for some parts of the Pacific, with yellow fever a risk in Ecuador. Papua New Guinea is a high-risk malaria area, and precautions are also needed against typhoid and polio.
A good book to consult if you want to know what the weather will be like or what to pack when you travel abroad is Weather To Travel, which covers 205 countries. Published by Tomorrow's Guides, it costs £6.99 from bookstores.
Because we cocoon ourselves in modern forms of transport and accommodation it is easy to think ourselves immune to the dangers of the outside world. Yet they are very real.
The trend towards holidaying further afield and to more remote countries has been matched by an increase in travellers returning with exotic diseases such as yellow fever, hepatitis, typhoid - and malaria. And with many of the top diving areas in the malarial and yellow fever belts, the risk to divers is particularly great.
In tropical and sub-tropical areas, malaria is one of the world's biggest killers. An estimated 2 million people a year die from the mosquito-borne disease, and according to the Medical Advisory Service for Travellers Abroad, the incidence of malaria contracted by people returning to the UK has grown significantly and represents some 2,000 cases a year.
The disease is also spreading into new areas such as Turkey and further into the Indian sub-continent and South America. Chloroquine-resistant strains have spread to most areas except the Middle East and parts of Central America, which is why a number of different regimens to guard against it are now needed, depending on destination.
Recent bad publicity about the side-effects of Lariam, which contains mefloquine, has meant that some people are now unwilling to take it, even though it is the most effective drug to combat malaria strains endemic in many countries.
Remember the ABC of malaria:
Be aware of the risk. No prevention measure guarantees effectiveness against malaria.
Avoid being bitten. Sleep in a screened room and use a spray to kill mosquitoes that enter by day. Use mosquito nets at night, even better if they are pyrethroid-impregnated. Use an electric vapouriser with anti-insect tablets at night. Wear long sleeves and long trousers outdoors after sunset (mosquitoes bite only during the evening and at night). And use repellents containing diethyl toluamide (DEET) on exposed skin and clothing. Apply liberally and frequently.
Take appropriate chemoprophylaxis - preventive drugs - for one week before travel, during your stay and for four weeks after return.
Any fever or flu-like symptoms within a year of overseas travel, and particularly within the first three months, could be malaria. Seek medical help immediately. Malaria can kill if not treated quickly.
